Convection-recirculation heater



- June 24, 1969 B, 5 BURRUS 3,451,378

CONVECTLON- RECIRCULATION HEATER Filed Aug. 31, 1967 OUTLET INVENTOR. BILL S, BURRUS ATTORNEY B. S. BURRUS June 24, 1969 CONVECTION-EH31RCULATION HEATER I Fi led Aug. 51,

OUTLET PLENUM CHAMBER l4 INVENTOR. BILL 3.

EUR us BY ATTORNEY B. S. BURRUS June 24, 1969 CONVECTION-RECIRCULATION HEATER Sheet Filed Aug. 31, 1967 1N VENTOR BILL s. BURRUS ATTORNEY United States Patent 3,451,378 CONVECTION-RECIRCULATION HEATER Bill S. Burrus, Tulsa, Okla, assignor to Combustion Engineering, Inc., New York, N.Y., a corporation of Delaware Filed Aug. 31, 1967, Ser. No. 664,839 Int. tCl. F22b 15/00; F233 5/02 US. Cl. 122-235 4 Claims ABSTRACT OF THE DISCLOSURE A combustion chamber is shown with products of combustion developed in it from a burner. The products flow into indirect heat exchange with a fluid requiring heat and a passage is provided to recirculate a portion of the cooled products and mix them with the hot initial products from the combustion chamber.

BACKGROUND OF THE INVENTION Field of the invention The present invention relates to heaters whose products of combustion are forced into indirect heat exchange with fluids to be heated, and the products recirculated. More specifically, the invention relates to forced distribution of the products through the heat exchange section, control of the quantity of products recirculated and positive mixing of the recirculated products with the initial products.

Description of the prior art Direct fired, indirect, heaters are well known. The products of combustion, generated by burning various kinds of fuels, are flowed over the external surface of conduits containing fluids requiring heat. The heat of the products of combustion is thereby transferred to the fluids in the conduits. Also, it is known to recirculate some por- It is a principal object of this invention to release all of the heat from a burner in one chamber and force the products of combustion through a second chamber in which conduits are mounted for fluids which require heat.

It is another object to control the direction of the flow of the products to prevent channelling, or stratification, of the products in the heat exchange chamber.

Another object is to recirculate a portion of the cooled products from the heat exchange chamber to a mixing chamber through which products of the burner chamber pass, the recirculated products being controlled to limit the surface temperature of the conduits for fluid, mounted in the heat exchange chamber.

Another object is to limit the flame of the burner to the burner chamber and turbulate the burner products as they flow into the mixing chamber and are mixed with the recirculated products.

The invention contemplates an elongated combustion chamber which is horizontally extended. A burner is mounted in one end to direct products of combustion along the length of the chamber. A mixing chamber is connected to the discharge end of the combustion chamber, and a wall is arranged to partially separate the two chambers in order to limit the burner flame to the combustion chamber and to induce turbulence in the products as they flow into the mixing chamber. The mixing chamber receives both the initial products and recirculated products to combine them for flow into a heat exchange chamber. The mixture is directed over heated conduits mounted in the heat exchange chamber so as to militate against channelling. The quantity of the cool recirculated products flowed from the heat exchange chamber back into the mixing chamber is controlled to limit the temperature of the surface of the heated conduits.

Other objects, advantages and features of this invention will become apparent to one skilled in the art upon consideration of the written specification, appended claims, and attached drawings, wherein:

FIG. 1 is a perspective side elevation of the complete heater system embodying the invention with the heat exchange section slightly exploded from the combustion chamber;

FIG. 2 is a partially sectioned perspective side elevation of the heat exchange section;

FIG. 3 is a section of the mixing chamber of FIG. 1;

FIG. 4 is a section of the mixing chamber of FIG. 1;

FIG. 5 is a diagrammatic representation of the system to illustrate the controls in the system.

DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1 was established to illustrate the overall organization of the chambers of the heating system and their sizes relative to each other. The drawings are not of visualized structure but are taken from an actual reduction of practice which was constructed and tested during the drafting of this application.

It was decided that FIG. *1 would use a perspective view to show the complete unit, but with the heat exchange chamber slightly exploded from the combustionmixing chamber unit so as to give a partial view of the conduit system for the products of combustion flowing into the bottom of the heat exchange chamber.

All the structure is arranged about the combustion chamber in Which the products of combustion are released. The chamber is embodied in an elongated, horizontally extended shell 10. This shell is sectioned to show it lined with refractory throughout its length. A burner 11 is mounted in one end. This burner had the usual supplies of fuel and air. Nothing more than a common, well-known, type and make of burner and associated equipment is contemplated for this service.

A mixing chamber 12 is mounted on the second end of shell 10. All of the initial products of combustion flow from the combustion chamber and into this mixing chamber. Products of combustion which have given up heat to the conduits to be heated are partially recirculated. These products are also brought to mixing chamber 12 and combined with the initial products.

The heat exchange chamber 13 is fairly large, relative to the combustion chamber. It is comprised of a boxshaped shell extending along the combined lengths of both the combustion and mixing chambers. Careful planning was required to force the enormous quantity of heated gases from the mixing chamber through the heat exchange chamber 13 without channelling, or stratification. A plenum chamber 14 is part of the conduit system between the mixing and heat exchange chambers. From this plenum chamber, the combined gases are divided into separate conduits along the lower length of chamber 13.

Two conduits 15, 16 are connected between plenum chamber 14 and heat exchange chamber 13. More such conduits might be desirable in some sizes. However, in the actual reduction to practice, two conduits give ade- 3 quate horizontal distribution along the length of chamber 13. Conduit 15 is clearly seen in both FIG. 1 and FIG. 2. FIG. 1 does not show conduit 16, located behind combustion chamber 10.

After the products flow up through chamber 13, a portion of them is drawn through conduit 17. Blower 18 is the prime mover provided for this function. The products drawn through conduit 17 are forced along conduit 19 and distributed in mixing chamber 12. The products not recirculated are discharged to atmosphere through stacks 20.

CONTROL SYSTEM FIG. 5 has been established to give a broad understanding of the variables of the heater and the control exerted over them. The chambers 10, 12 and 14 are combined to show that the products of combustion flow from them and into heat exchange chamber 13. These products which are discharged from chamber 13 through stacks 20 are recirculated through conduits 17 and 19.

The heated fluid conduits are depicted in chamber 13. Fluid is pumped through these conduits from some source and delivered to some point of use. The temperature of the heated fluid flowing from the conduit system is sensed and applied to control the combustion fuel and air to the burner of the heater. Therefore, the heat demand is met by regulating the combustion heat release from the burner 11.

The baflling within chamber 13 must be arranged to militate against channeling the products of combustion as they flow over the conduit system. Obviously it is desirable to apply heat evenly over the surface of the conduits. To initiate this even distribution, the products of combustion must be divided into a multiplicity of streams which are individually routed into chamber 13. Conduits 15 and 16 represent the plurality of passages for the multiplicity of streams. Dampers 30, 31 are mounted in these conduits and regulate the portion of the products of combustion each of the conduits 15 and 16 flow from the heater into chamber 13. Wall 32 maintains the basic distribution from the conduits and 16. Other walls, bafl les and diverters not shown complete the distribution to obtain the uniformity of heating desired.

The skin temperature of the heated fluid conduits in chamber 13 is of great concern. Failure of heated conduits in other heater designs is usually the result of excessive temperature. The improved distribution of the heating medium in this heater militates against failure from this cause. However, direct control of the temperature of the heating medium is necessary to insure that the critical temperature of the conduit skin is not exceeded. Therefore, bulb 33 is mounted in conduit 16, one of the conduits taking the heating medium to chamber 13, to directly sense the temperature of the products of combustion. Conventional controls respond to the signal generated by b'ulb 33. Damper 34 is regulated by this generated signal.

Damper 34 controls the quantity of the products of combustion discharged from chamber 13 which are recirculated to combine with the initial products of combustion produced by burner 11. The cooler products discharged from chamber 13 reduce the final temperature of the medium flowing into chamber 13 as desired. The result is a selected upper limit for the skin temperature of the conduit system in chamber 13.

In operation, it is contemplated that a fluid requiring heat will be pumped through the conduit system mounted in chamber 13. The rate of this fluid flow may vary, but the temperature to which the fluid is heated will be sensed continuously. The sensed temperature will continually regulate the fuel and air supplied to burner 11, insuring that heat will be released in chamber 10 which can raise the fluid to a selected temperature.

The heat released is distributed through chamber 13. The distribution is controlled basically by the initial regulation of conduits 15 and 16 with their dampers 30 and 31. The various partitions, diverters and baflies Within chamber 13, including wall 32, complete the distribution so that the efficiency of heat transfer will not be restricted by lack of even exposure of the fluid to the heating medium.

It is not presently practical to release precisely the amount of heat which will elevate the temperature of the fluid to the level desired and prevent the skin temperature of the conduit section from becoming excessive. The temperature to which the fluid is heated will vary with changes in the rate of fluid flow and the ability of the fluid to absorb heat in chamber 13. This variable of the final temperature should basically establish the heat released and available for absorption. However, the practical skin temperature limits represents other factors which must modify the heat presented to the fluid for absorption.

The temperature of the products of combustion, as they flow to the skin of the conduit section, must be sensed and applied to meter out the heat released to the exchange process. Therefore, the recirculation system is controlled by the temperature sensed at 33. The temperature guarded at this point insures that within the practical limits of the conduit material to Withstand continuously applied heat, the demand for the heat will be met by the system.

HEAT EXCHANGE CHAMBER 13 Both FIGS. 1 and 2 disclose the plan to pass the fluid to be heated through a plurality of parallel branch conduits within chamber 13. This arrangement basically enlarges the surface of fluid conduit to be heated to, in effect, increase the distribution of heat within chamber 13.

Inlet conduit 40 is brought to the heater and connected to a manifold pipe 41. A plurality of branches (two are shown) are connected to manifold 41 and extended in reaches the horizontal length of chamber 13. Manifold pipe 42 is connected to the other ends of these branch conduits and outlet conduit 43 connected to mainfold 42.

The foregoing arrangement of conduits gives horizontal distribution of the conduits as well as vertical distribution. With fins mounted on the branch conduits, the products of combustion must traverse a complicated, intricate path from the bottom of chamber 13 to the top. The very complication of this maze promotes uniform distribution of the products of combustion through the volume of chamber 13.

MIXING CHAMBER 12 The overall, and complete, flow pattern of fluids through the structure, and their control, has been disclosed. FIGS. 3 and 4 are to be coordinated with FIG. 1 to disclose the unique provisions for mixing the initial products of combustion from burner 11 with those products of combustion recirculated from heat exchange chamber 13. The temperature of the mixture is controlled by regulation of the quantity of the recirculated products of combustion.

It is desirable to efliciently contain the combustion process within shell 10. That is, it is very desirable to isolate the conduits for the products of combustion from direct flame impingement and its radiant heat. Certainly it is most desirable to take into heat exchange chamber 13 only the readily controlled products of combustion for utilization of their convective heat. Otherwise, the high temperatures generated by radiant heat of the burner flame will accelerate failure of the conduits and the heat exchange chamber structure.

Wall 50 is mounted on the interior of the discharge end of the combustion chamber to, first, limit the burner flame to the combustion chamber.

The Wall 50 is extended upwardly from the side of the combustion chamber in a plane normal to the path of the burner flame as the flame is propagated down the length of shell 10. The wall is high enough for the flame to impinge upon it and limit the flame to the combustion chamber and therefore isolate the conduits for the products of combustion from direct flame impingement and its radiant heat.

Second, wall 50 is sized and arranged so that the products of combustion, flowing over it to exit from the combustion chamber, will have turbulence induced in them. With the recirculated products of combustion distributed into chamber 12, mixing of the initial products of combustion and the recirculated products is greatly facilitated. The temperature of the resulting mixture quickly varies in accordance with the quantity of recirculated products regulated into the efficient mixing within chamber 12. Therefore, wall 50 both isolates the radiant heat of the combustion chamber from subsequent structure and deflects the products of combustion into a turbulent pattern for efficient mixing.

Distribution of the recirculated products of combustion from conduit 19 in chamber 12 is facilitated by the structural arrangement disclosed most clearly in FIGS. 3 and 4. A manifold 51 is saddled over the upper portion of chamber 12. Connected to conduit 19, this manifold 51 receives the products of combustion and introduces them into chamber 12 through a plurality of openings 52. The result is a wide distribution of the recirculated products of combustion into the turbulated products of combustion flowing from the combustion chamber. Eflicient mixing of the two streams of fluid results.

The very multiplicity of passages connecting manifold 51 and chamber 12 distributes the recirculated products. Additionally, the openings are formed as slots, apparent in FIGS. 1 and 4. Through these slots 52 the products flow into chamber 12 over a wide area. The products of combustion, deflected upward from the combustion chamber, sweep into turbulated collision with the downflowing recirculated products of combustion. Efficient mixing of the two streams of fluid results.

The mixture of fluids, turbulent and homogeneous, descends through chamber 12 and roars out into plenum chamber 14 for the fundamental distribution provided by conduits 15 and 16. No prior art recirculation heater has provided this eflicient mixing and isolation which promotes eificient control of the skin temperature of the heat exchange surfaces and their protection from radiant heat.

From the foregoing it will be seen that this invention is one well adapted to attain all of the ends and objects hereinabove set forth, together with other advantages which are obvious and which are inherent to the apparatus.

It will be understood that certain features and subcombinations are of utility and may be employed without reference to other features and subcombinations. This is contemplated by and is within the scope of the claims.

As many possible embodiments may be made of the invention without departing from the scope thereof, it is to be understood that all matter herein set forth or shown in the accompanying drawings is to be interpreted as illustrative and not in a limiting sense.

The invention having been described, what is claimed 1s:

1. A heater for fluids including, an elongated combustion chamber horizontally extended, v

a burner mounted on a first end of the combustion chamber to direct flame and products of combustion the length of the chamber,

a deflector wall mounted on the interior wall of the second end of the chamber normal the path of the burner flame to receive the impact of the burner flame of the combustion chamber in limiting the burner flame to the combustion chamber and inducing turbulence in the products of combustion flowing from the combustion chamber,

a mixing chamber connected to the second end of the combustion chamber to receive the turbulated prod ucts of combustion from the combustion chamber and provide a volume in which they mix with recirculated products of combustion,

a plenum chamber connected to the mixing chamber to conduct the combined products of combustion to heat exchange,

a heat exchange chamber connected to the plenum chamber with a plurality of openings,

means for controlling the flow of products of combustion from the plenum chamber to distribute the products within the heat exchange chamber in a predetermined pattern,

a conduit system extending through the heat exchange chamber to convey fluids requiring heat into indirect contact with the products of combustion, and

a conduit connecting the heat exchange chamber and the mixing chamber to recirculate a predetermined quantity of the products of combustion.

2. The heater of claim 1 in which the connecting conduit has means for controlling the amount of products recirculated to limit the surface temperature of the heated fluid conduit system.

3. A heater for fluids including,

an elongated combustion chamber horizontally extended,

a burner mounted on a first end of the combustion chamber to direct products of combustion the length of the chamber,

a mixing chamber connected to the second end of the combustion chamber to receive the products of combustion from the combustion chamber and provide a volume in which they mix with recirculated products of combustion,

a heat exchange chamber connected to the mixing chamber,

a conduit system extending through the heat exchange chamber to convey fluids requiring heat into indirect contact with the products of combustion, and

a conduit connecting the heat exchange chamber and the mixing chamber with a plurality of openings to recirculate a predetermined quantity of the products of combustion.

4. The heater of claim 3 in which the connecting conduit has means for controlling the amount of products recirculated to limit the surface temperature of the heated fluid conduit system.

References Cited UNITED STATES PATENTS 1,896,910 2/1933 Merkt. 1,901,922 3/ 1933 Mekler. 1,938,699 12/ 1933 Huet.

FOREIGN PATENTS 565,345 3/1958 Belgium. 589,031 12/1933 Germany.

CHARLES I. MYHRE, Primary Examiner.

US. Cl. X.R. 431- 

